The present invention relates generally to actuators and, in an embodiment described herein, more particularly provides an actuator for a downhole tool.
Many types of actuator systems have been used for controlling operation of tools in subterranean wells. Some of the more common are hydraulic actuators which operate in response to pressure in control lines and electrical actuators which operate in response to signals transmitted via wires.
Each of these has enjoyed success in appropriate circumstances. However, each also has its drawbacks which prevent its use in other circumstances, or which prevent more widespread use of the system. For example, downhole hydraulic actuators which use control lines to transmit pressure from the surface typically require large pressures to be transmitted to overcome flow resistance in the control lines, compensate for hydrostatic pressure in the control lines, etc. As another example, downhole electrical actuators which use wires to transmit electrical power from the surface are limited in the amount of electrical power that can be transmitted by the wires due, for instance, to the electrical resistance of the wires.
What is needed is an actuator system which may be reliably operated downhole, and which does not require transmission of high pressures or large amounts of electrical power for its operation.
In carrying out the principles of the present invention, in accordance with an embodiment thereof, an actuator system is provided which utilizes a gas absorptive material. The gas absorptive material expands when it absorbs gas and contracts when it discharges gas. Associated actuation methods are also provided.
In one aspect of the invention, an actuator is provided which includes a metal hydride powder in a chamber. When hydrogen gas is introduced into the chamber, the powder absorbs the gas and expands. Expansion of the powder may be used to displace a member, such as a piston of the actuator. Displacement of the piston may be used to displace a fluid to actuate a device, such as a downhole tool.
In another aspect of the invention, absorption of gas by the gas absorptive material and discharge of gas from the gas absorptive material may be controlled in various manners. For example, a gas flow controller may be used to control the flow of gas between the chamber and a gas storage device. The gas flow controller may be a valve connected between the gas storage device and the chamber, or it may be a heating device.
A heating device may be used to control flow of gas in different ways. For example, heating the gas absorptive material may cause it to discharge gas. As another example, the gas storage device may include a gas storing material which, when heated, discharges gas. Thus, gas may be made to flow in a desired direction by heating either the gas absorptive material or the gas storing material.
In yet another aspect of the invention, contraction of the gas absorptive material due to discharge of gas as a result of an increase in temperature of the gas absorptive material may be used to operate mechanisms in unique manners. For example, the gas absorptive material may have an expanded volume at the surface due to absorption of gas therein. However, when the material is positioned in a well, the increased temperature in the well may cause the gas absorptive material to discharge the gas, resulting in the material contracting in volume. This contraction of the material may be used to operate a downhole device. The use of well temperature to contract the material ensures that the device will not be operated at the surface.
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings.